The present invention relates to magnetic materials, including a novel iron oxide-containing magnetic material exhibiting unusually high coercive force.
The magnetic properties of the ferrimagnetic iron oxides Fe.sub.3 O.sub.4 and gamma-Fe.sub.2 O.sub.3 have long been of interest for applications such as magnetic recording materials and the like. U.S. Pat. No. 2,694,656 discusses the preparation, physical characteristics and magnetic properties of these oxides and their use in the manufacture of magnetic tape recording materials.
Magnetic iron oxide may be prepared in bulk and subsequently applied to a suitable support or it may be produced in situ on the support. U.S. Pat. No. 2,919,207 discloses a process of the latter type wherein a ferrimagnetic coating is applied to a moving support directly from a vapor phase incorporating iron carbonyl.
The size and shape of the iron oxide particles are known to be factors affecting the magnetic properties thereof. U.S. Pat. No. 3,015,627 suggests that the size and shape of gamma-ferric oxide crystallites directly affect the coercivity and remanence of the bulk oxide.
Composition can also play an important role in determining the magnetic properties of iron oxides. As disclosed in U.S. Pat. No. 3,996,395, there is a range of composition in the system of gamma Fe.sub.2 O.sub.3 -Fe.sub.3 O.sub.4 solid solutions wherein coercivities approaching 1000 Oe have been observed.
It has been proposed, for example in U.S. Pat. Nos. 4,150,173 and 4,199,614, to produce a porous glass-supported ferrimagnetic iron oxide material by the solution phase thermal decomposition of iron carbonyl in the presence of porous glass. The product is porous glass containing metallic iron, which can then be oxidized to gamma-Fe.sub.2 O.sub.3 if desired. When oxidized, the product is characterized as a ferrimagnetic material with relatively small magnetic remanence and coercive force.